Various cyanine dyes and merocyanine dyes have conventionally been known. Examples thereof are described in, for example, F. M. Hamer, Cyanine Dyes and Related Compounds (Ed. A. Weissberger, 1964, Wiley Interscience (New York)); G. E. Ficken, The Chemistry of Synthetic Dyes, vol. 4, Chapter V, 1971 (Ed. K. Venkataraman, Academic Press (New York and London)); and D. M. Sturmer, The Chemistry of Heterocyclic Compounds (Ed. A. Weissberger and E. C. Taylor, 1977, John Wiley and Sons (New York)). These compounds adsorb a heavy metal or heavy metal ion, but have disadvantages such as transferring, diffusion and elution when they are used as dyes. A compound which can adsorb a heavy metal or a heavy metal ion strongly has been desired.
The chromogen structure of the cyanine dyes comprises two of the so-called basic nuclei linked to each other through a conjugated double bond chain. However, those cyanine dyes which have as substituent linked to this cyanine chromogen structure a nitrogen-containing heterocyclic group or groups, particularly a nitrogen-containing heterocyclic group or groups capable of chemically or physically adsorbing a heavy metal such as silver ion, have not been known.
Likewise, the chromogen structure of the merocyanine dyes comprises a so-called acidic nucleus and a basic nucleus linked to each other through a conjugated double bond chain. However, those merocyanine dyes which have as a substituent linked to this merocyanine chromogen structure a nitrogen-containing heterocyclic structure or structures, particularly a nitrogen-containing heterocyclic structure or structures capable of chemically or physically adsorbing a heavy metal such as silver ion, have not been known.